Conventionally, in electronic circuit apparatuses such as electronic keys used, for example, for smart key-less entry, the case of each apparatus is partially made of a transparent resin and the light emitted from an LED that indicates an operating state of the electronic key passes through this resin (e.g., see Patent Literature (hereinafter, referred to as “PTL”) 1. In addition, electronic keys in recent years are required to be shock-resistant, water-resistant and thinner, and card-type electronic keys each formed by sealing a circuit board with a thermosetting resin have been developed (e.g., see PTL 2).